Under natural viewing conditions, circuits in primary visual cortex (V1) must represent the information contained in a continuous stream of images that often contains abrupt changes in stimulus properties. Here we use voltage-sensitive dye imaging to explore how changes in the direction of stimulus motion are represented in the dynamics of V1 population response. Full-field random dot patterns whose direction of motion changed instantaneously from 0 to 180 degrees are used as visual stimuli.

In order to characterize the direction of motion specified by the cortical activity pattern, population response profiles were generated by convolving stimulus evoked VSD maps with the direction preference map for a given region of cortex. We found that dynamics of the population response vary as a function of direction deviation angle. For direction deviation angles smaller than 90°, the peak direction sweeps smoothly from the initial direction to the final direction. For direction deviation angles larger than 112.5°, the peak direction transiently deviates away from the direction of the second stimulus, then exhibits a step function that transiently overshoots and then settles on the final direction. Dynamics of peak amplitude also vary as a function of direction deviation angle. There is often a “notch” during the transition which is largest when the direction deviation angles are near 90°.

The dynamics of the population response predict distortions in the perceived direction of stimulus motion that depend on the angle of deviation. For a small direction deviation angle, the perceived motion trajectory is predicted to be smoother than the real stimulus trajectory. In contrast, for a large direction deviation angle, the perceived motion trajectory is predicted to be sharper than the real stimulus trajectory. Preliminary results from studies of human perception suggest distortions in the perception of motion trajectory that are consistent with these predictions.